As a main renewable technology, photovoltaic power generation technology is widely used in many countries and regions. In photovoltaic power generation technology, a photovoltaic panel is used to absorb solar energy and convert the solar energy into direct current, and through maximum power tracking by the photovoltaic inverter, the maximum direct current outputted by the photovoltaic panel is converted into alternating current for the use of loads.
The photovoltaic power generation technology is directly related to sunray. With the gradual enhancement of solar irradiance in the morning, the voltage outputted by a photovoltaic array rises. The photovoltaic inverter begins grid-connected operation when the voltage reaches a startup voltage needed for the photovoltaic inverter to operate. With the gradual weakening of solar irradiance at sunset, open-circuit voltage and energy of the photovoltaic panel gradually decrease, and at the moment, the power outputted by the photovoltaic inverter gradually reduces. In a case that the power outputted by the photovoltaic inverter is lower than a predetermined threshold, the photovoltaic inverter tries to shut down, disconnecting a grid-side relay.
At present, the method for startup control of a photovoltaic inverter includes determining the startup of the photovoltaic inverter based on the magnitude of the input voltage of the photovoltaic panel PV, i.e., in a case that the input voltage is greater than a predetermined threshold, starting the relay into grid-connected operation. However, according to this method, only the magnitude of the input voltage is considered, while the magnitude of the input energy is not considered. Problems of repeated startup and shutdown occur, which greatly affects the service life of the grid-connected relay.